[
While the fire protection of structural steel for new builds is well documented, what is not so well understood is the best approach to take for its repair, renovation or reinstatement. Bill Parlor tells us more.
When considering refurbishment using fire resisting boards, sprayed mineral coatings, or reactive coatings, the first step is to establish the fire resistance requirement of the structural steel frame. This will involve Building Control or other relevant approval bodies and/or reference to Approved Document B: Fire Safety. Secondly, the existing fire protection system needs to be identified and its manufacturer contacted to assess the likely fire resistance contribution, and its suitability for continued use. Depending on the findings, all areas and parts of the system that are shown to be unsuitable should be repaired, over-clad or removed, before being replaced with a system capable of fulfiling the new fire resistance requirements.
This article is intended to clarify matters and to provide guidance on the subject, but it is important to note that it applies only to materials listed in the current ASFP publication Fire Protection for Structural Steel (also known as the Yellow Book).
Because the fire protection installer is not in control of any off-site or previous preparation of steelwork, before work begins, the client and the main contractor and/or structural engineer should approve all steel as ready for the refurbishment process and for the installation of the required fire protection to begin. If the degree of corrosion is severe, it may be necessary to ensure the steelwork itself remains fit for purpose. Also, after steelwork is exposed during the refurbishment process, the steel condition should be inspected again, before the installation of any fire protection.
In general, there are five separate refurbishment approaches that could be considered:
Full removal of all existing protection and replacement with a new system to meet the required specification. ASFP TGD Codes 11, 14 and 15 will provide details for the entire installation process depending on whether the new protection system is based on reactive coatings, fire protection boards, or sprayed mineral coatings. (TGD 14 and 15 will be published mid 2009.)
Removal of damaged protection or those parts that fail to meet the new requirements and replacement with the same protection system. Where necessary, consider the compatibility of the existing and new system components, any additional surface preparation requirements and any other specific measures to be undertaken, such as fixing and jointing techniques.
Part removal and replacement with a different system. In such situations (in order to maintain the performance of the overall protection), careful assessment must be made to areas where these different systems interface, such as jointing details. It is recommended that such detailing is confirmed by the manufacturer and/or competent authority for the intended works. The ASFP considers it best practice to completely protect individual steel or structural elements with the same fire protection system. Mixing of fire protection systems should be avoided on single elements.
Over-cladding/refurbishment with the same system. Remove any damaged in-situ fire protection which may affect the ‘stickability’ of the new system – damaged areas should be repaired in accordance with the manufacturer’s instructions. Ensure that the combined thickness of the refurbished protection does not exceed the maximum permissible thickness for the system. For board and spray systems, guidance should be obtained from the manufacturer for the entire refurbishment system and fixings. Likewise, guidance should be sought from the manufacturer for reactive systems before adding any additional layers. The presence of an existing top coat, for example, may affect the advice provided.
Over-cladding/refurbishment with a different system. Again, the ASFP considers it best practice to completely protect individual steel or structural elements with the same system. Ideally, the mixing of fire protection systems should be avoided on single elements, but this is not always possible. If mixing of fire protection systems is unavoidable, then depending on the nature of the existing and new fire protection systems, the following guidance should be followed:
Over-cladding one fire protection board system with another type of board. As these types of boards are generally inert, there are usually no concerns regarding their compatibility, but the compatibility of any component with adhesives, or glues, or different metals, will need evaluation by the manufacturer.
It is not acceptable to simply add the contributions of the different systems together in order to arrive at an overall fire resistance performance, since their individual contribution in such circumstances cannot be considered in isolation. Since the contribution of an existing system cannot be usefully quantified, the required fire resistance should be provided in its entirety by the additional protection. The new fire protection system should also be fixed in a manner recommended by the manufacturer.
Over-cladding an existing and identified sprayed mineral coating with a fire protecting board system. The new boards must be adequately and independently fixed to offer the required protection period – refer to the board system manufacturer for confirmation and to agree the most suitable fixing method. Again, it is not acceptable to simply add the contributions of the different systems together in order to arrive at an overall fire resistance performance, since their individual contribution in such circumstances cannot be considered in isolation. Since the contribution of an existing system cannot be usefully quantified, the required fire resistance should be provided in its entirety by the additional protection
Adding protection over an existing and identified sprayed mineral coating system with a different sprayed mineral coating system. First, identify the existing system, since the mixing of spray systems should be avoided wherever possible. Check the chemical compatibility of existing and new products with both manufacturers and if acceptable, over-spray in accordance with their recommendations, provided that the new layers are adequately fixed and independently supported. Once again, it is not acceptable to simply add the contributions of the different systems together in order to arrive at an overall fire resistance performance.
Adding protection over an intumescent (reactive) coating system with a board or sprayed mineral coating system. If any over-cladding is to be added to steelwork, which is already protected from fire by an intumescent coating systems, then:
– In general, a minimum gap of 50 times the dry film thickness of the reactive coating is recommended, to allow adequate expansion of the reactive coating in the event of a fire. This applies to the gap between the cladding and the flat surfaces of the protected steel, as well as flange tips, unless specific fire test data proves otherwise.
– Gap sizes may be reduced where the coating manufacturer has specific fire test evidence to justify the reduction.
– Continuous linear fixings/spacers, in timber or metal, should be considered as part of the main steel section and duly protected from fire, unless specific fire test evidence can be provided to justify alternative action. Alternatively, where a completely new fire protection system is being applied – and independently fixed and supported over an existing intumescent reactive coating – the new cladding system should provide all the required fire resistance by itself, without consideration of any residual contribution from the original reactive coating.
Adding protection to a board or sprayed mineral coating system with an intumescent (reactive) coating system. Any special solution should only be considered on the basis of specific fire test and assessment data for the type of steel sections concerned.
Pass it on
In accordance with Building Regulations, following completion of the work ensure that all records concerning the refurbishment – including manufacturer’s literature and inspection records – are passed to the client’s Responsible Person, who is liable for the fire risk assessment and the maintenance of fire safety of the building and its occupants. Such information should be maintained in the building log book to allow the safe management of the building and facilitate future changes.
Guidance information on the suitability, selection, use and maintenance of passive fire protection is provided in the ASFP publication Ensuring Best Practice for Passive Fire Protection in Buildings. Specific guidance on fire protection for structural steel is provided in the ASFP Yellow Book. Technical Guidance Document 8 provides guidance for junctions between different fire protection systems when applied to load bearing structural steel elements, while Technical Guidance Document 10 provides guidance for the refurbishment and upgrading of fire protection to structural steelwork.
Current versions of all ASFP documents are available for download from www.asfp.org.uk without charge. Alternatively, hard copies can also be provided at a nominal charge from the ASFP, Tournai Hall, Evelyn Woods Road, Aldershot GU11 2LL. Tel: 01252 357832. Fax: 01252 357831. Email: info@asfp.org.uk
While the fire protection of structural steel for new builds is well documented, what is not so well understood is the best approach to take for its repair, renovation or reinstatement. Bill Parlor tells us more.
When considering refurbishment using fire resisting boards, sprayed mineral coatings, or reactive coatings, the first step is to establish the fire resistance requirement of the structural steel frame. This will involve Building Control or other relevant approval bodies and/or reference to Approved Document B: Fire Safety. Secondly, the existing fire protection system needs to be identified and its manufacturer contacted to assess the likely fire resistance contribution, and its suitability for continued use. Depending on the findings, all areas and parts of the system that are shown to be unsuitable should be repaired, over-clad or removed, before being replaced with a system capable of fulfiling the new fire resistance requirements.
This article is intended to clarify matters and to provide guidance on the subject, but it is important to note that it applies only to materials listed in the current ASFP publication Fire Protection for Structural Steel (also known as the Yellow Book).
Because the fire protection installer is not in control of any off-site or previous preparation of steelwork, before work begins, the client and the main contractor and/or structural engineer should approve all steel as ready for the refurbishment process and for the installation of the required fire protection to begin. If the degree of corrosion is severe, it may be necessary to ensure the steelwork itself remains fit for purpose. Also, after steelwork is exposed during the refurbishment process, the steel condition should be inspected again, before the installation of any fire protection.
In general, there are five separate refurbishment approaches that could be considered:
Full removal of all existing protection and replacement with a new system to meet the required specification. ASFP TGD Codes 11, 14 and 15 will provide details for the entire installation process depending on whether the new protection system is based on reactive coatings, fire protection boards, or sprayed mineral coatings. (TGD 14 and 15 will be published mid 2009.)
Removal of damaged protection or those parts that fail to meet the new requirements and replacement with the same protection system. Where necessary, consider the compatibility of the existing and new system components, any additional surface preparation requirements and any other specific measures to be undertaken, such as fixing and jointing techniques.
Part removal and replacement with a different system. In such situations (in order to maintain the performance of the overall protection), careful assessment must be made to areas where these different systems interface, such as jointing details. It is recommended that such detailing is confirmed by the manufacturer and/or competent authority for the intended works. The ASFP considers it best practice to completely protect individual steel or structural elements with the same fire protection system. Mixing of fire protection systems should be avoided on single elements.
Over-cladding/refurbishment with the same system. Remove any damaged in-situ fire protection which may affect the ‘stickability’ of the new system – damaged areas should be repaired in accordance with the manufacturer’s instructions. Ensure that the combined thickness of the refurbished protection does not exceed the maximum permissible thickness for the system. For board and spray systems, guidance should be obtained from the manufacturer for the entire refurbishment system and fixings. Likewise, guidance should be sought from the manufacturer for reactive systems before adding any additional layers. The presence of an existing top coat, for example, may affect the advice provided.
Over-cladding/refurbishment with a different system. Again, the ASFP considers it best practice to completely protect individual steel or structural elements with the same system. Ideally, the mixing of fire protection systems should be avoided on single elements, but this is not always possible. If mixing of fire protection systems is unavoidable, then depending on the nature of the existing and new fire protection systems, the following guidance should be followed:
Over-cladding one fire protection board system with another type of board. As these types of boards are generally inert, there are usually no concerns regarding their compatibility, but the compatibility of any component with adhesives, or glues, or different metals, will need evaluation by the manufacturer. It is not acceptable to simply add the contributions of the different systems together in order to arrive at an overall fire resistance performance, since their individual contribution in such circumstances cannot be considered in isolation. Since the contribution of an existing system cannot be usefully quantified, the required fire resistance should be provided in its entirety by the additional protection. The new fire protection system should also be fixed in a manner recommended by the manufacturer.
Over-cladding an existing and identified sprayed mineral coating with a fire protecting board system. The new boards must be adequately and independently fixed to offer the required protection period – refer to the board system manufacturer for confirmation and to agree the most suitable fixing method. Again, it is not acceptable to simply add the contributions of the different systems together in order to arrive at an overall fire resistance performance, since their individual contribution in such circumstances cannot be considered in isolation. Since the contribution of an existing system cannot be usefully quantified, the required fire resistance should be provided in its entirety by the additional protection.
Adding protection over an existing and identified sprayed mineral coating system with a different sprayed mineral coating system. First, identify the existing system, since the mixing of spray systems should be avoided wherever possible. Check the chemical compatibility of existing and new products with both manufacturers and if acceptable, over-spray in accordance with their recommendations, provided that the new layers are adequately fixed and independently supported. Once again, it is not acceptable to simply add the contributions of the different systems together in order to arrive at an overall fire resistance performance.
Adding protection over an intumescent (reactive) coating system with a board or sprayed mineral coating system. If any over-cladding is to be added to steelwork, which is already protected from fire by an intumescent coating systems, then:
– In general, a minimum gap of 50 times the dry film thickness of the reactive coating is recommended, to allow adequate expansion of the reactive coating in the event of a fire. This applies to the gap between the cladding and the flat surfaces of the protected steel, as well as flange tips, unless specific fire test data proves otherwise.
– Gap sizes may be reduced where the coating manufacturer has specific fire test evidence to justify the reduction.
– Continuous linear fixings/spacers, in timber or metal, should be considered as part of the main steel section and duly protected from fire, unless specific fire test evidence can be provided to justify alternative action. Alternatively, where a completely new fire protection system is being applied – and independently fixed and supported over an existing intumescent reactive coating – the new cladding system should provide all the required fire resistance by itself, without consideration of any residual contribution from the original reactive coating.
Adding protection to a board or sprayed mineral coating system with an intumescent (reactive) coating system. Any special solution should only be considered on the basis of specific fire test and assessment data for the type of steel sections concerned.
Pass it on
In accordance with Building Regulations, following completion of the work ensure that all records concerning the refurbishment – including manufacturer’s literature and inspection records – are passed to the client’s Responsible Person, who is liable for the fire risk assessment and the maintenance of fire safety of the building and its occupants. Such information should be maintained in the building log book to allow the safe management of the building and facilitate future changes.
Guidance information on the suitability, selection, use and maintenance of passive fire protection is provided in the ASFP publication Ensuring Best Practice for Passive Fire Protection in Buildings. Specific guidance on fire protection for structural steel is provided in the ASFP Yellow Book. Technical Guidance Document 8 provides guidance for junctions between different fire protection systems when applied to load bearing structural steel elements, while Technical Guidance Document 10 provides guidance for the refurbishment and upgrading of fire protection to structural steelwork.
Current versions of all ASFP documents are available for download from www.asfp.org.uk without charge. Alternatively, hard copies can also be provided at a nominal charge from the ASFP, Tournai Hall, Evelyn Woods Road, Aldershot GU11 2LL. Tel: 01252 357832. Fax: 01252 357831. Email: info@asfp.org.uk